How to track grocery price increases

A bigger grocery bill can mean prices went up, or it can mean you bought more. The total can't tell you which. To see price changes you need the same items, measured the same way, at two points in time. That takes a short list, a notebook or spreadsheet, and the receipts you already get.

01Pick a basket of staples

Choose 8 to 15 things you buy at least once a month. Staples work best because you see them often: coffee, milk, eggs, bread, cereal, rice or pasta, canned tomatoes, a fruit you always buy, toilet paper, dish soap. Skip one-off purchases. A price you see once is a data point, not a trend.

Be specific. Write down the brand and the size, not just “coffee”. If you switch brands halfway through, you are measuring your choices, not the store's prices. Keep the same product on the list for as long as you keep buying it.

• Item, with brand and size as printed on the pack
• Shop and date
• Price you paid for one pack (or the price per pound for loose produce)
• Size of the pack: ounces, pounds, fluid ounces, count, or sheets
• Unit price: price divided by size
• Whether it was on sale that week

02Record the unit price, not the sticker price

The unit price is the price divided by the amount you get. A 12 oz bag of coffee at $8.99 costs 8.99 ÷ 12 = $0.749 an ounce. That number lets you compare a 12 oz bag with a 10.5 oz bag, or a 14 oz box with an 18 oz box, on equal terms.

Pick one unit per item and stick to it. Ounces for dry goods, fluid ounces or gallons for drinks, pounds for loose produce, count for eggs, and sheets for paper products. Loose produce is the easy case: the receipt usually prints the weight and the price per pound, so the unit price is already there. For packaged goods you need the size from the pack or the shelf tag, because receipts often abbreviate it or leave it out. The guide on how to read a grocery receipt covers the abbreviations and weight lines.

Mark sale prices. A two-week promotion that takes 20% off makes the product look 25% more expensive when it ends, though the regular price never moved. Compare regular price with regular price, and note the sale separately.

03Watch the pack size

Sometimes the price stays put and the pack gets smaller. This is often called shrinkflation, and it only shows up if you track the size. The US Bureau of Labor Statistics handles it this way in the Consumer Price Index: where size is recorded, it divides the price by the size to get an effective price, usually per ounce. Its own example is a candy bar that goes from 1.6 oz to 1.5 oz at the same price. The UK's Office for National Statistics uses a chocolate bar that shrinks from 85 g to 80 g. At the same price, that is 85 ÷ 80 = 1.0625, a 6.25% rise per gram.

Across all prices, the effect is small. BLS estimated that size changes added about 0.01% a year to its all-items index. It is concentrated in certain products, though. Household paper goods had more size changes than any other category BLS studied, with 716 reports from 2015 to 2021, about 3% of the price observations for that category. ONS found weight changes happen most often in food. If your basket is heavy on paper towels, cereal, snacks, or chocolate, your own numbers can move more than the national average.

04A worked example: two receipts six months apart

Here are two trips to the same store, one in March and one in September. The basket is the same seven items. The coffee bag and the toilet paper sheet count changed; the shelf price of both did not.

Before tax, the subtotal went from $37.41 to $38.46, up 2.8%. That looks mild. It also hides two things: the bananas weighed more in September, and two items got smaller at the same price. Line the items up by unit price instead.

Now price the March basket at September unit prices. Keep the March amounts: 12 oz of coffee, 2 lb of bananas, 3,168 sheets of toilet paper. Coffee is 12 × $0.856 = $10.27. Toilet paper is 3,168 × $0.0044365 = $14.05. Bananas are 2 × $0.65 = $1.30. Add the cereal ($4.79), eggs ($3.49), milk ($3.99) and tomatoes ($2.78), and the same basket costs $40.67 in September against $37.41 in March. That is a rise of 8.7%, about three times what the subtotals suggested.

That like-for-like number is your personal grocery inflation for this basket. It won't match the national figure, and it shouldn't. It reflects what you buy and where you shop.

05Compare stores by unit price

The same method works across shops. Take the same items and compare unit prices, not sticker prices. The cheaper-looking pack is not always the cheaper product.

The Northgate cereal box costs 80 cents less, but you get 4 oz less, so each ounce costs more. The bigger coffee bag costs more up front and less per ounce. A bigger pack only saves money if you use it before it goes stale or spoils. For more on turning these comparisons into savings, see how to save money on groceries with your receipts.

06Keep the log going

1. 1Keep grocery receipts for a month in one envelope or photo album.
2. 2Once a month, copy the tracked items into your log: date, shop, size, price, unit price.
3. 3When a size on the pack differs from last time, write the new size and flag it.
4. 4Every three months, price your original basket at today's unit prices and compare it with the first month.
5. 5When one item stands out, check its unit price at a second store before you switch.

Ten minutes a month is enough. The log also gives you a better starting point for a food budget than any national average, because it is built from your own prices. The guide on how to set a grocery budget picks up from there.

07How Sorayli tracks prices from your receipts

Sorayli builds a price tracker from the receipts you scan. When a scan finishes, each product line is saved with its shop, date, quantity and unit price. The unit price is what you paid for one: the price printed on the line, or the line total divided by the quantity when none is printed. If the receipt has a discount on the whole order, it is spread across the lines first. Fee lines such as bag fees are left out. A receipt whose lines don't add up to its total is left out of the tracker too, so one misread price column can't distort your history. Expenses you type in by hand have no line items, so they are not part of it.

• A product is tracked once it appears on receipts at least a week apart. Two lines on the same receipt don't count as a history.
• For each tracked product it compares the first price with the latest one over the past 12 months, and lists the biggest rises and falls.
• Basket inflation is the average change across products you bought in both halves of that year, weighted by what you spend on each.
• Receipts in another currency are converted to your base currency at a daily exchange rate for the receipt date, so prices from a trip abroad compare with prices at home. See multi-currency.

In the iPhone app, the Price tracker screen lists every tracked product. Tap one to see its price history charted by shop, and, when you bought it at two or more shops, which shop is cheapest at its latest price. On the web, the analytics page shows your basket inflation and the top rising and falling products.

The price tracker is part of the Pro and Family plans. Pro is $9.99 a month or $69.99 a year; Family is $17.99 a month or $129.99 a year for up to 5 people. The Free plan includes 10 scans a month and does not include the price tracker. Plans are on the pricing section.